Electronic assemblies having embedded passive heat pipes and associated method

ABSTRACT

An electronic assembly may include a chassis, and electronic modules mounted within the chassis. Each electronic module may include a printed circuit substrate, heat-generating electronic components mounted on the printed circuit substrate, and a heat sink body mounted to the printed circuit substrate and having a plurality of heat pipe receiving passageways extending between opposing side edges and overlying corresponding heat-generating components. A respective elongate, passive, heat pipe may extend within each heat pipe receiving passageway and be removably fastened to at least one end to the heat sink body for enhanced conductive heat transport.

FIELD OF THE INVENTION

The present invention relates to the field of cooling electronicassemblies containing, but not limited to, printed circuit boards, andmore particularly, to cooling dissipating components contained withinthe chassis of an electronic assembly using heat sinks and passive heatpipes.

BACKGROUND OF THE INVENTION

As electronic packaging density increases and dissipated power increasesto achieve higher levels of electronic performance, the need forefficient thermal transport within electronic assemblies having printedcircuit boards is increasing. Brute force heat transfer techniquesinvolving forced air, active liquid cooling, and similar heat transportmechanisms have been used to transport heat from sensitive electroniccomponents to heat sinks or similar heat spreading devices. Some heattransfer systems use composite structures, for example, annealedpyrolytic graphite (APG) embedded within metallic skins, or use heatpipes that are physically connected to spreader plates by solder, epoxy,or clamps.

These heat transfer systems have benefits and shortcomings depending onthe application and environment. In the case of APG composites, in-planeconductivities are on the order of approximately 800-1000 W/m-K at endof life (EOL), but have much higher values at the beginning of life(BOL). This degradation over time is caused, for example, by thermalcycling. Through-plane conductivity is also a concern for APG compositesbecause graphite is orthotropic, and its through-plane conductivity ismuch lower because of the orientation of in-plane graphite fibers.Despite this in-plane conductivity being six times that of aluminum andtwo and a half times that of copper, this conductivity is still inferiorto that of a typical water-filled copper heat pipe having greater than10,000 W/m-K in its vapor space, or about ten times that of graphite.

Most heat pipe applications are received in hemispherical grooves andthen flattened for direct contact with high heat generating components.In an active heat transfer system, a condenser end of the heat pipe mayterminate to permit heat removal, often via fan convection. This type ofactive heat dissipation may provide good heat transport, but dedicatedheat spreaders or heat sinks are required to reduce thermal gradientsand improve the conductive transport between the heat sources and heatsink. This technique, however, is not always practical. The heat pipesare exposed to the elements leading to corrosion and often requirecomplex geometries. Other heat pipe designs require clamps, which canintroduce undesirable risks or complexity due to heat pipe deformationwith respect to clamp load, integration difficulty, and overall designrepeatability. These issues impact performance and reliability of theelectronic assembly and their integration to printed circuit boards andassociated components.

SUMMARY OF THE INVENTION

In general, an electronic assembly may include a chassis, and aplurality of electronics modules mounted within the chassis. Eachelectronics module may comprise a printed circuit substrate, a pluralityof heat-generating electronic components mounted on the printed circuitsubstrate, and a heat sink body mounted to the printed circuitsubstrate. The heat sink may have opposing ends and opposing side edgesextending between the opposing ends, and the heat sink body may have aplurality of heat pipe receiving passageways extending therethroughbetween opposing side edges and overlying corresponding ones of theheat-generating components. The electronics module may also include arespective elongate, passive, heat pipe extending within each heat pipereceiving passageway and be removably fastened to at least one end tothe heat sink body.

Each of the heat-receiving passageways may be continuous so that eachelongate, passive, heat pipe is concealed within the heat sink body. Theheat sink body may have a plurality of weight relief recesses thereinbetween adjacent heat pipe receiving passageways, for example.

In some embodiments, each heat pipe receiving passageway may include athreaded end portion, and each elongate, passive, heat pipe has a matingthreaded end removably fastened to the threaded end portion of acorresponding heat pipe receiving passageway. In other embodiments, theassembly may comprise a respective removable fastener removablyfastening each elongate, passive, heat pipe within the correspondingheat pipe receiving passageway.

The heat sink body, in some embodiments, may comprise a 3D printed heatsink body. In other embodiments the heat sink body may comprise a 3Dprinted heat sink body, and each elongate, passive, heat pipe maycomprise a 3D printed heat pipe.

The chassis structure may comprise additional elongate, passive, heatpipes extending therein using integration techniques previouslydescribed. In addition, each elongate, passive, heat pipe may comprise asolid rod.

Another aspect is directed to a method for making a thermally enhancedelectronics module to be mounted within a chassis. The method mayinclude mounting a plurality of heat-generating electronic components ona printed circuit substrate, and mounting a heat sink body to theprinted circuit substrate and having opposing ends and opposing sideedges extending between the opposing ends. The heat sink body may have aplurality of heat pipe receiving passageways extending therethroughbetween opposing side edges and overlying corresponding ones of theheat-generating components. The method also includes removably fasteninga respective elongate, passive, heat pipe extending within each heatpipe receiving passageway. The method may include applying a thermalinterface material between each heat pipe and the respective heat pipereceiving passageway.

DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome apparent from the detailed description of the invention whichfollows, when considered in light of the accompanying drawings in which:

FIG. 1 is an isometric view of an electronic assembly showingelectronics modules utilizing printed circuit substrates mounted withinits chassis in accordance with an example embodiment.

FIG. 2 is an isometric view of the electronics module mounted to aheatsink body and integral to the assembly shown in FIG. 1 .

FIG. 3 is a top plan view of the electronics module shown in FIG. 2 .

FIG. 4 is an isometric view of the electronics module of FIG. 2 showingweight relief recesses on the heat sink.

FIG. 5 is an isometric view of a side wall from the chassis of FIG. 1and showing heat pipes extending therein.

FIG. 6 is an exploded isometric view of a threaded end of the heat pipeshown in FIG. 5 .

FIG. 7 is a flow diagram illustrating method aspects associated with theassembly of an electronics module consisting of a printed circuit boardand embedded heat pipe heatsink body of FIG. 2 .

DETAILED DESCRIPTION

The present description is made with reference to the accompanyingdrawings, in which exemplary embodiments are shown. However, manydifferent embodiments may be used, and thus, the description should notbe construed as limited to the particular embodiments set forth herein.Rather, these embodiments are provided so that this disclosure will bethorough and complete. Like numbers refer to like elements throughout,and prime notation is used to indicate similar elements in differentembodiments.

Referring initially to FIG. 1 , an electronic assembly 30 includes achassis 32 formed as an enclosure having a top wall 32 a, bottom wall 32b and side walls 32 c. As illustrated, a section of its top wall 32 a isremoved to show a plurality of electronic modules 34 containing printedcircuit boards that are mounted within the chassis 32. In thisnon-limiting example, the chassis 32 may be formed from differentmetallic or non-metallic materials, such as aluminum or thermoplasticmaterials, and is configured to receive electronic modules 34 as a 3Uform factor. The illustrated four corner brackets 40 engage a panel orother mounting surface 42 to mount the electronic assembly 30 on thesurface as a self-contained unit. The electronic assembly 30 may includedifferent types of connectors contained within its chassis 32, such as abackplane connector or other circuit board connector, to which theprinted circuit boards contained within the plug-in electronic modules34 may interface. Other connectors 44 in this example are positioned ona side wall 32 c of the chassis 32 to which cables, wires or otherelectrical connectors may extend into the chassis 32 and connect to theelectronic modules 34.

Referring now to FIGS. 2-4 , there is illustrated an example embodimentof an electronic module 34 as mounted in the chassis 32 of theelectronic assembly 30 of FIG. 1 . The module 34 includes a printedcircuit substrate 50 having a plurality of heat-generating electroniccomponents 52 mounted on the printed circuit substrate as best shown inthe plan view of the electronic module in FIG. 3 . Such heat-generatingelectronic components 52 may include microprocessors, field programmablegate arrays (FPGA's), and similar electronic components that generateheat during their operation and are interconnected to each other throughvias and electronic circuit traces formed on the printed circuitsubstrate 50. In this example, a circuit card connector 54 is mounted atthe end of the printed circuit substrate 50 and configured to connectthe electronic module 34 into a backplane connector or other circuitboard connector contained within the chassis 32. The printed circuitsubstrate 50 can be formed using standard manufacturing techniques knownto those skilled in the art. In this example, the printed circuitsubstrate 50 is designed to conform to the VITA 3U form factor andconfigured to fit within the illustrated chassis 32. In a non-limitingexample, the printed circuit substrate 50 is rectangular configured.

A heat sink body 60 is mounted to the printed circuit substrate 50 andhas opposing ends 62 and opposing side edges 64 extending between theopposing ends. The heat sink body 60 can be formed from different heatconductive materials, such as aluminum, but can also be formed as a 3Dprinted heat sink body using additive manufacturing techniques as willbe explained in greater detail below. The heat sink body 60 includes aplurality of heat pipe receiving passageways 70 extending therethroughbetween opposing side edges 64 and overlying correspondingheat-generating electronic components 52. The passageways 70 may beformed by standard manufacturing processes known to those skilled in theart, including boring or other techniques. A respective elongate,passive heat pipe 72 extends within each heat pipe receiving passageway70 and is removably fastened to at least one end as the side edge 64 ofthe heat sink body 60, such as by a heat pipe fastener or close-outattached to an end of a respective heat pipe described below. The heatpipes 72 extend transverse through the heat sink body 60 and overlie thecorresponding heat-generating components 52. Each heat-receivingpassageway 70 is continuous so that each elongate, passive, heat pipe 72is concealed within the heat sink body 60. Each heat pipe receivingpassageway 70 may include a threaded end portion 74 (FIG. 4 ) and eachelongate, passive, heat pipe 72 has a mating threaded end removablyfastened to the respective threaded end portion 74 of the correspondingheat pipe receiving passageway 70. In the illustrated example, the heatpipes may be restrained using a compression plug on both ends as aclose-out, or a set screw or similar device. This demonstrates theversatility for installing pipes using separate fastening hardware(e.g., set screws or compression plugs) for mechanical attachment toreceiving structure.

Although the illustrated embodiment uses a mating threaded end orcompression plug, it is possible that helicoils could be installed tohold the heat pipes 72 or self-tapping fasteners used. It is alsopossible to press-fit each heat pipe 72 into a passageway 70.

A plurality of interstitial materials, commonly referred to asreworkable thermal interface materials, may be used between the heatpipe and receiving passageway. The use of a material at this interfacewill reduce the thermal resistance between the heat-generatingcomponents and the transport medium, in this case the heat pipe andintegral vapor space. Typical materials that can be used are cured andnon-curing silicone suspensions, thermal epoxies and greases, solder,and others. Use of an interstitial material does not influence thefastening approach outlined herein and is used as an optionalenhancement to the overall thermal management solution.

Each heat pipe may act as a stiffening member in the receivingstructure. This provides dual-use mechanical and thermal benefits withextensibility to metal and ceramic matrix composites (MMC and CMCs)where strength to weight ratio must be optimized with thermal transportcapability.

In a non-limiting example, each electronic module 34 may include arespective removable fastener 80 as a close-out, for example, such asbest shown in FIGS. 2, 3 and 6 , which removably fastens each elongate,passive heat pipe 72 within a corresponding heat pipe receivingpassageway 70. In the example shown in FIG. 6 , the fastener 80 may bepress-fit onto the end of the heat pipe 72 and may include an end 82that is configured to receive a tool, allowing a manufacturer to insertthe heat pipe into the heat pipe receiving passageway 70 and screw thefastener within the heat pipe receiving passageway, thus locking theheat pipe within the passageway. In another embodiment, the fastener 80could be bonded or soldered to the heat pipe 72. This removable fastener80 may be formed as integral threads on the body of the pipe in yetanother example.

Each elongate, passive heat pipe 72 may be formed as a hollow or solidrod and constructed from a conductive material, such as, but not limitedto, copper or brass. The fasteners 80 may be formed from the same ordifferent material as the heat pipe 72, and in an example, is a separatestainless steel fastener secured onto the end of the passive heat pipe.

The heat sink body 60 preferably includes a plurality of weight reliefrecesses 86 formed therein between adjacent heat pipe receivingpassageways 70 (FIG. 4 ) as concealed pipe areas and operate to reducethe overall weight of the heat sink body. It is understood that thechassis 32 receives a number of electronic modules 34 to form theelectronic assembly 30. The electronic modules 34 with their associatedprinted circuit substrates 50, heat-generating electronic components 52and heat sink bodies 60 will add weight to the electronic assembly 30.The weight relief recesses 86 formed in each heat sink body 60 reducethe overall weight of the electronic assembly 30. This weight reduction,even though slight per module 34, becomes important when there arenumerous electronic assemblies 30 that operate together in one device orcraft. This can be done without any sacrifice to thermal performance dueto the efficiency of the thermal transport within the heat pipes vs.additional mass required to lower lateral thermal resistance through asolid material.

Referring now to FIG. 5 , there is illustrated at least one side wall 32c removed from the chassis 32 and having a plurality of elongate,passive heat pipes 90 received within heat pipe receiving passageways 92that extend vertically within the side wall of the chassis. In thisexample, the heat pipes 90 received within the side wall 32 c are formedsimilar to those heat pipes 72 received within the passageways 70 of theheat sink body 60, but in this illustrated example, the side wall heatpipes 90 have only one fastener 94 that removably fastens the heat pipe90 into a threaded end portion 96 of the side wall 32 c of the chassis32. In this example, these “first” heat pipes 90 connected into thechassis side wall 32 c may include only one fastener 94, while the“second” heat pipes 72 received within the heat sink body 60 and shownrelative to FIGS. 2-4 may include fasteners 80 at both ends such as setscrews or other fastener devices.

It has been found that the heat pipes 90 received in the passageways 92of the side wall 32 c of the chassis 32 can reduce temperatures by asmuch as 10° to 15° C. and may outperform APG composite designs by afactor of five in a 3U form factor as a non-limiting example. This isbased on a weight-neutral basis for the material that integrates theheat pipes 90 and which material can be subsequently removed in otherareas since the heat transport is handled by the embedded heat pipes andis not dependent upon the material thickness, which would otherwise berequired to reduce the lateral thermal resistance.

The heat pipes 72 concealed within the heat sink body 60 and heat pipes90 concealed within the side wall 32 c have no impact on the module formor fit. It has been found that this design as described facilitatesfabrication of the electronic modules 34 and permits assembly in underfour weeks in a typical design fabrication cycle, versus a 12-16 weeklead time for APG and other complicated active heat pipe approaches thatrequire pumps and associated devices for fluid flow.

This design as described provides robustness because the heat pipes 72are completely concealed in the heat sink body 60, or as in the case ofthe heat pipes 90, they are concealed in the side wall 32 a of thechassis 32. This design provides reworkability since the heat pipes72,90 may be removed if necessary. The heat pipes 72,90 improve thermaltransport capability with additional surface area for heat uptake andtransport making the heat pipes easier to integrate into a systeminstead of a state-of-the-art APG or fluid flow via active heat pipedesigns.

Referring now to FIG. 7 , there is illustrated a flowchart for a methodof making the electronic modules 34 to be mounted within a chassis 32.The process starts (Block 100) and a plurality of heat-generatingelectronic components 52 are mounted onto a printed circuit substrate 50(Block 102).

The heat sink body 60 is mounted to the printed circuit substrate 50,which includes its opposing ends 62 and opposing side edges 64 extendingbetween the opposing ends (Block 104). This heat sink body 60 has aplurality of heat pipe receiving passageways 70 extending therethroughbetween opposing side edges 64 and overlying correspondingheat-generating electronic components 52. The respective elongate,passive heat pipes 72 extending within each heat pipe receivingpassageway 70 may be removably fastened to the heat sink body 60 (Block106) such as using set screws or other threaded fasteners as an example.The process ends (Block 108).

As noted before, it is possible to form the heat sink body 60 and heatpipes 72 using 3D printing, i.e., using additive manufacturingtechniques. Different additive manufacturing techniques may be used toform the 3D printed heat sink body and the associated 3D printed heatpipes. It is possible to use Fused Deposition Modeling (FDM), includinga process that feeds filaments of metal wire or other material throughan extrusion nozzle head to build various layers. Laser sinteringtechniques, including selective laser sintering with metals and polymersand direct metal laser sintering, may be employed. It is also possibleto use electron beam melting and melt metal powder, layer by layer,using the electron beam while employed in a high vacuum. It is alsopossible to use stereo lithography techniques with photo polymerization.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

1-24. (canceled)
 25. A method for making an electronic module to bemounted within a chassis, the method comprising: 3D printing a heat sinkbody; coupling the 3D printed heat sink body to a plurality ofheat-generating electronic components on a circuit substrate, the 3Dprinted heat sink body having opposing ends and opposing side edgesextending between the opposing ends, the 3D printed heat sink bodyhaving a plurality of heat pipe receiving passageways extendingtherethrough between opposing side edges and overlying correspondingones of the heat-generating components; 3D printing a plurality of heatpipes; and fastening a respective 3D printed heat pipe extending withineach heat pipe receiving passageway.
 26. The method according to claim25, wherein each heat pipe receiving passageway is continuous so thateach corresponding 3D printed heat pipe is concealed within the 3Dprinted heat sink body.
 27. The method according to claim 25, wherein 3Dprinting the heat sink body comprises forming at least one weight reliefrecess adjacent at least one heat pipe receiving passageway.
 28. Themethod according to claim 25, wherein 3D printing the heat sink bodycomprises forming a plurality of weight relief recesses adjacent theheat pipe receiving passageways.
 29. The method according to claim 25,wherein each heat pipe receiving passageway includes a threaded endportion; and wherein fastening comprises fastening each 3D printed heatpipe with a mating threaded end to the threaded end portion of acorresponding heat pipe receiving passageway.
 30. The method accordingto claim 25, comprising applying a thermal interface material betweeneach 3D printed heat pipe and the respective heat pipe receivingpassageway.
 31. The method according to claim 25, wherein fastening therespective 3D printed heat pipe includes attaching a fastener to an endof each 3D printed heat pipe.
 32. The method according to claim 25,wherein each 3D printed heat pipe comprises a passive 3D printed heatpipe.
 33. The method according to claim 25, wherein 3D printing the heatsink body comprises at least one of Fused Deposition Modeling (FDM),laser sintering, electron beam melting, and stereo lithography.
 34. Themethod according to claim 25, wherein 3D printing the heat plurality ofheat pipes comprises at least one of Fused Deposition Modeling (FDM),laser sintering, electron beam melting, and stereo lithography.
 35. Themethod according to claim 25, wherein the plurality of 3D printed heatpipes comprise a material to impart stiffness to the 3D printed heatsink.
 36. A method for making an electronic module to be mounted withina chassis, the method comprising: 3D printing a heat sink body by FusedDeposition Modeling (FDM); coupling the 3D printed heat sink body to aplurality of heat-generating electronic components on a circuitsubstrate, the 3D printed heat sink body having opposing ends andopposing side edges extending between the opposing ends, the 3D printedheat sink body having a plurality of heat pipe receiving passagewaysextending therethrough between opposing side edges and overlyingcorresponding ones of the heat-generating components; 3D printing aplurality of heat pipes by FDM; and fastening a respective 3D printedheat pipe extending within each heat pipe receiving passageway.
 37. Themethod according to claim 36, wherein each heat pipe receivingpassageway is continuous so that each corresponding 3D printed heat pipeis concealed within the 3D printed heat sink body.
 38. The methodaccording to claim 36, wherein 3D printing the heat sink body comprisesforming at least one weight relief recess adjacent at least one heatpipe receiving passageway.
 39. The method according to claim 36, whereineach heat pipe receiving passageway includes a threaded end portion; andwherein fastening comprises fastening each 3D printed heat pipe with amating threaded end to the threaded end portion of a corresponding heatpipe receiving passageway.
 40. The method according to claim 36,comprising applying a thermal interface material between each 3D printedheat pipe and the respective heat pipe receiving passageway.
 41. Themethod according to claim 36, wherein fastening the respective 3Dprinted heat pipe includes attaching a fastener to an end of each 3Dprinted heat pipe.
 42. The method according to claim 36, wherein each 3Dprinted heat pipe comprises a passive 3D printed heat pipe.
 43. A methodfor making an electronic module to be mounted within a chassis, themethod comprising: 3D printing a heat sink body with at least one weightreducing recess therein; coupling the 3D printed heat sink body to aplurality of heat-generating electronic components on a circuitsubstrate, the 3D printed heat sink body having opposing ends andopposing side edges extending between the opposing ends, the 3D printedheat sink body having a plurality of heat pipe receiving continuouspassageways extending therethrough between opposing side edges andoverlying corresponding ones of the heat-generating components; 3Dprinting a plurality of heat pipes; and fastening a respective 3Dprinted heat pipe extending within each heat pipe receiving passageway.44. The method according to claim 43, wherein each heat pipe receivingcontinuous passageway includes a threaded end portion; and whereinfastening comprises fastening each 3D printed heat pipe with a matingthreaded end to the threaded end portion of a corresponding heat pipereceiving continuous passageway.
 45. The method according to claim 43,comprising applying a thermal interface material between each 3D printedheat pipe and the respective heat pipe receiving passageway.
 46. Themethod according to claim 43, wherein fastening the respective 3Dprinted heat pipe includes attaching a fastener to an end of each 3Dprinted heat pipe.
 47. The method according to claim 43, wherein each 3Dprinted heat pipe comprises a passive 3D printed heat pipe.
 48. Themethod according to claim 43, wherein 3D printing the heat sink bodycomprises at least one of Fused Deposition Modeling (FDM), lasersintering, electron beam melting, and stereo lithography; and wherein 3Dprinting the heat plurality of heat pipes comprises at least one ofFused Deposition Modeling (FDM), laser sintering, electron beam melting,and stereo lithography.